[BANGKOK] Scientists have edged closer to a dengue vaccine following trials in Thailand, where dengue fever is endemic, that have shown a vaccine candidate to be safe and effective, although more evidence is needed to prove its effectiveness.

The results of the clinical phase II trial, showing the vaccine to be 30 per cent effective in protecting from dengue, were published in The Lancet last week (11 September). The vaccine CYD-TDV, which was developed by the drug company Sanofi Pasteur, has been tested on 4,000 children aged four to 11 from 57 schools in Thailand's Muang District.

Dengue fever is the world's most widespread mosquito-borne viral disease with around half of the global population at risk. There is no vaccine to protect against it, although there are several being developed.

It is difficult to develop an effective vaccine because dengue fever is caused by four different strains of virus — known as DENV 1, 2, 3 and 4. The challenge is to develop a vaccine that can protect against all types of dengue virus.

"The results of this trial show that the vaccine can protect against dengue fever caused by three virus types [DENV 1, 3 and 4]," said Pascal Barollier, a Sanofi Pasteurspokesperson. "The vaccine was well tolerated and safe, with no serious effects on those who received it."

But scientists not involved with the study say there is not enough data to prove the vaccine's effectiveness against severe dengue disease, and urged for further, larger trials.

Scott Halstead, a physician at the International Vaccine Institute in Seoul, Republic of Korea, said the result was both "surprising and disappointing", pointing out that the vaccine does not protect against DENV 2, "the most common type in Thailand".

He said it is too early to draw any conclusions about the vaccine's safety.

Sutee Yoksan, director of the Center for Vaccine Development at Mahidol University in Thailand, shared Halstead's concerns, and called for further investigations.

According to Barollier, phase III clinical studies involving 31,000 children and
adolescents are ongoing in Latin America (Brazil, Colombia, Honduras, Mexico and Puerto Rico) and in five
Asian countries (Indonesia, Malaysia, the Philippines, Thailand and Vietnam) where dengue is endemic.

These trial results are expected in 2014. If successful the vaccine could be available in 2015 in countries where dengue is a public health priority.